Walnuts, like those grown on Russ Lester’s Dixon Ridge Farms in Winters, California, are some of agriculture’s most energy-intensive crops given the amount of product you get from them. The inedible shell constitutes 50 to 60 per cent of each nut, and has conventionally just been discarded. On Dixon Ridge’s 400 acres, that translates into about 2.5 million pounds (more than 1200 tons) of shell waste annually. But rather than pay someone to dispose of these shells, Lester instead converts them into syngas using a cadre of downdraft gasifiers built by the Community Power Corporation of Englewood, CO.

Known as the BioMax, these machines can transmogrify a variety of woody biomass, and even some plastics, into nitrogen-diluted syngas. This includes everything from wood chips and pellets to orange and grape skins, cardboard and product packaging to kitchen waste and plastic utensils. Anything with less than 25 per cent moisture can undergo gasification.

The BioMax system relies on pyrolysis (greek for “fire separation”) to convert biomass into syngas, the same process used to make charcoal. Organic material is placed in an anaerobic environment and heated to a minimum of 200C — 300C. This causes the material to separate into gas and liquid components, leaving a solid residue of char. In the BioMax system, the resulting gas is a mix of ~17 per cent hydrogen, 20 per cent carbon monoxide, 8 per cent carbon dioxide, 2 per cent methane and the remainder nitrogen (all of which can be separated, bottled, and either used on-site or sold). It also leaves behind char-ash, a carbon-rich fertiliser. What’s more, this char-ash is created from some of the CO2 produced by the process, resulting in a net-loss of carbon.